Administration of pyridostigmine (Mestinon) to a patient with a history of urticaria to this drug in the past

1/8/2013
I recently evaluated an 84 yo WM with history of myastenia gravis and atrial fibrillation for drug allergy. Several years ago, he developed a diffuse urticarial rash within 2 hours of taking Mestinon and was diagnosed with a "bromide" allergy. No other systemic symptoms were present. Over the past several years he has successfully taken Mytelase (ambenonium chloride) without difficulty. However, Mytelase is no longer being manufactured. At this time, his neurologist wants him to resume Mestinon and referred him for desensitization.

Assuming he has a bromide sensitivity, are you aware of any published reports of successful desensitization to Mestinon? Thank you.

A:

Thank you for your inquiry.

Allergic reactions to pyridostigmine (Mestinon) must be extremely rare. I was only able to find one such report in the literature (1). In this instance, an oral challenge was performed which reproduced symptoms consistent with an immediate hypersensitivity reaction, but there was no confirmation of an IgE-mediated event by skin testing or in vitro testing. This patient was not desensitized, and I was not able to find any reports of desensitization to pyridostigmine or, as mentioned, any other cases.

Pyridostigmine is available in a syrup. Therefore one could easily do a graded oral challenge to this drug. The decision to do so, of course, would be one based on a risk/benefit analysis which should only be made by discussing the issues with the patient and the neurologist.

If you do decide to proceed, graded doses would be administered every two hours. I would start with 1/1,000th of the prescribed dose, and double the dose every two hours. This means that the procedure would take more than one day if done in your office.

Of course, precautions need to be taken that the cumulative dose, given during the oral challenge, does not at any time exceed the suggested therapeutic dose.

Since we have not documented that the patient is truly allergic to pyridostigmine (other than by history), this would actually be a graded oral challenge rather than a desensitization procedure per se.

Thank you again for your inquiry and we hope this response is helpful to you.